Preparation of zinc salts of 4-tert-butyl-thiophenol



United States Patent 3,215,716 PREPARATION OF ZINC SALTS OF 4-TERT-BUTYL-THIOPHENOL Martin B. Neuworth and Donald C. Jones, Pittsburgh, Pa., and Joseph A. Kohlbeck, Salt Lake City, Utah, assignors to Consolidation Coal Company, Pittsburgh, Pa., a corporation of Pennsylvania No Drawing. Filed Oct. 19, 1962, Ser. No. 231,817 4 Claims. '(Cl. 260429.9)

This invention relates to an improved process for preparing zinc salts of aryl mercaptans. It particularly relates to the preparation of zinc 4-t-butylthiophenoxide.

The zinc salts of aryl mercaptans are known in the art as chemical plasticizers for butadiene-styrene elastomers and other elastomeric materials, producing peptized polymers of lowered viscosity and enhanced malleability. Zinc 4-t-butylthiophenoxide in solid form is a particularly effective peptizer. Various fillers and extenders may ordinarily be incorporated with the solid peptizer in commercial use.

In US. Patent 2,413,531, it has been proposed to prepare the zinc salts of aryl mercaptans by reacting an aryl mercaptan with zinc oxide in an inert organic solvent. This method is disadvantageous commercially where it is proposed to recover the zinc salt of the aryl mercaptan in the solid state because of the necessity for substantially complete removal of the organic solvent. This requirement for solvent recovery of highly volatile solvents presents various equipment problems and explosion hazards.

It has been known that the zinc salts of aryl mercaptans may be prepared by reacting a water-soluble alkali mercaptide with a water-soluble zinc salt. However, this method has been considered to be of laboratory interest only and unsuitable for commercial exploitation. As pointed out in US. Patent 2,413,531: It has been found that this method for producing the zinc salts of the aromatic mercaptans is quite expensive because it involves several distinct steps and requires the use of large-volume equipment, for the solutions employed must be dilute. It has also been found that the resulting zinc salts of the mercaptans are obtained in such a very fine state of subdivision that they are difficult to filter, and therefore they are difficult to wash free from impurities so that the final product usually contains relatively large amounts of the inorganic salts which, in many cases, are detrimental to the subsequent use of the zinc salts of the aryl mercaptans. In most cases these salts must be dried and ground before they are in suitable physical form for use, which also requires special apparatus and utilization of considerable time in preparing them.

It is an object of this invention to overcome the known difficulties inherent in prior art processes and to provide a new, improved method for preparing the zinc salts of aryl mercaptans in excellent yields and in a high state of purity. The present process affords the first commercial method for preparing the zinc salts of aryl mercaptans in commercial yields using Water-soluble reactants.

In accordance with this invention, it has been found that the zinc salts of aryl mercaptans can be prepared by the metathetic interchange between water-soluble aryl mercaptides and water-soluble zinc salts, while maintaining a reaction temperature above 80 C., preferably be tween 90 and 100 C. Preferred aryl mercaptides for use in this process are the water-soluble alkali-metal or alkaline earth salts of the aryl mercaptans of the benzene and naphthalene series. The sodium mercaptide salt will generally be employed commercially because of its convenience, low cost, and ready water solubility. Preferred alkyl-substituted mercaptans are the lower alkylsubstituted mercaptans of the benzene series, such as 4-t- 3,215,716 Patented Nov. 2, 1965 butylthiophenol, o-thiocresol, 4-t-butyl-o-thiocresol, etc. Thiophenol may also be employed.

Any convenient water-soluble salt of zinc may be employed such as zinc sulfate, zinc acetate, zinc nitrate, or zinc chloride. Because of its ready availability and low cost, zinc chloride will ordinarily be employed commercially.

It is an essential and critical feature of this invention that it can be practiced on a commercial scale only if a minimum reaction temperature of C. is maintained during the course of the metathetic interchange. If, during the course of the reaction, the temperature drops below this determined critical value, gelation occurs, phase separation is no longer feasible, and filtration becomes impossible. Advantageously, using this process, a maximum total solids content between 25 and 40 Weight percent may be used without gelation occurring, higher concentrations being feasible at the higher temperatures, Thus avoidance of gelation rather than dispersion of a gel that is already formed is a significant feature of this invention.

By correlating solids content and temperature and maintaining vigorous agitation, the formation of a gel phase may be completely avoided. Once gelation occurs, satisfactory recovery of product under commercially operable conditions becomes extremely diflicult. Thus prolonged heating, solution dilution, and breaking up of the gel by pulverization are required. Filtration rates become inordinately slow because of plugging of the filter pores.

The metathetic reaction is essentially quantitative in nature. Ordinarily, therefore, approximately equivalent amounts of the water-soluble aryl mercaptide and Watersoluble zinc salt are used, although an excess of either ingredient may be used. Generally a slight excess of about 5 to 10 percent by weight of the water-soluble zinc salt will be employed to insure complete conversion of the water-soluble aryl mercaptide. Both reactants are preferably each separately dissolved in water before mixing so as to insure rapid reaction. Vigorous agitation during mixing is preferred to insure a rapid reaction and avoidance of a gel phase. The zinc aryl marcaptide is formed as readily filterable fine discrete granules which settle readily. The zinc salt may be conveniently recovered from solution by decantation, filtration or centrifugation.

While temperatures above 100 C. may be employed by using superatmospheric conditions, these elevated temperatures offer no process advantage and would call for the use of pressurized equipment, which would be less desirable from a commercial point of view. Therefore, atmospheric reflux temperatures not above 100 C. are ordinarily employed and preferred and permit the use of a high solids content reaction while avoiding gel formation.

It is a particular and preferred feature of this invention that the zinc salt of 4-t-butylthiophenol, zinc 4-tbutylthiophenoxide, may be conveniently and preferably obtained by the metathetic interchange at a temperature above 80 C. between the sodium salt of 4-t-butylthiophenol and zinc chloride. The invention will be illustrated by reference to the preparation of this compound, although not restricted thereto.

Example A large-scale batch of the sodium salt was prepared by reacting 50.0 pounds (0.30 pound mole) of 4-tbutylthiophenol with a dilute sodium hydroxide solution (13.2 percent). The amount of sodium hydroxide present was 13.5 pounds (0.331 pound mole). The solution of the sodium salt of 4-t-butylthiophenol was heated to 100 C. and 24 pounds of zinc chloride (0.177

pound mole) as a zinc chloride solution of 20.7 weight percent was added at a rate so as not to undulylower the temperature of the solution. Twenty-two minutes was required to add the zinc chloride solution, during which time the temperature varied between 87 and 94C. The reaction temperature after zinc chloride addition was 92 C. A total solids content of approximately 33 weight percent was present. During the addition of the zinc chloride solution, vigorous stirring was maintained in order to prevent the possibility of gel formation. The reactants were maintained at a reflux temperature of approximately 90-95 C., with stirring, for 30 minutes after the zinc chloride solution had been added. The water-insoluble zinc salt of 4-t-butylthiophenol that was formed readily settled in the form of free-flowing discrete granules. The supernatant liquor was easily decanted, and the product was washed in the reactor three or four times to remove sodium chloride, the water being decanted from the zinc 4-t-butylthiophenoxide in each case.

After the final wash in the reactor, the product was transferred, in slurry form, to a vacuum filter and washed on the filter several times with hot water. The filter cake obtained contained 40 to 50 percent water after vacuum filtration. The zinc 4-t-butylthiophenoxide was then dried in a vacuum drier at approximately 26 inches of vacuum maintaining a shell temperature of 105 C. The dried final product as obtained contained 0.85 percent moisture and represented 97 percent of the theoretical yield.

The unexpected criticality of the reaction temperature was illustrated in another run, where the temperature of the solution fell to 74 C. during the addition of the zinc chloride solution. Thereupon, a gelatinous mass formed which stalled the stirrer motor. Upon heating the solution to 95 C. the gel broke up somewhat and stirring could be resumed. However, washing of the product from this run in the reactor was impossible since no phase separation occurred, the wash Water being incorporated in the gel structure.

According to the provisions of the patent statutes, we have explained the principle and preferred mode of operation of our invention and have illustrated and described what we now consider to represent its best embodiment. However, we desire to have it understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically illustrated and described.

We claim:

1. The process for preparing zinc 4-t-butylthiophenoxide readily filterable in aqueous solution, which comprises mixing in aqueous solution with vigorous agitation a water-soluble salt of 4-t-butylthiophenol and a watersoluble zinc salt, while maintaining a temperature above C. and a maximum solids content in the resulting mixture between 25 and 40 percent, to eifect a metathetic interchange between the two water-soluble salts whereby zinc 4-t-butylthiophenoxide is formed as a readily filterable water-insoluble salt, and recovering said zinc salt.

2. The process for preparing zinc 4-t-butylthiophenoxide readily filterable in aqueous solution, which comprises mixing in aqueous solution with vigorous agitation zinc chloride and the sodium salt of 4-t-butylthiophenol, while maintaining a temperature above 80 C. and a maximum solids content in the resulting mixture between 25 and 40 percent, to effect a metathetic interchange be tween the two salts whereby zinc 4-t-butylthiophenoxide is formed as a readily filterable salt, and recovering said zinc salt.

3. The process according to claim 2 wherein said temperature is maintained between 80 and C.

4. The process for preparing zinc 4-t-butylthiophenoxide readily filterable in aqueous solution, which comprises mixing in aqueous solution with vigorous agitation the sodium salt of 4-t-butylthiophenol and an aqueous solution of zinc chloride, while maintaining a temperature above 80 C. and a maximum solids content in the resulting mixture between 25 and 40 percent, refluxing the solution at a temperature between 80 and 100 C., whereby a metathetic interchange between the two salts occurs and zinc 4-t-butylthiophenoxide is formed as a readily filterable salt, filtering the zinc 4-t-butylthiophenoxide, drying the filter cake consisting of zinc 4-t-butylthiophenoxide, and recovering the zinc salt as a dried, granular product.

References Cited by the Examiner UNITED STATES PATENTS 2,454,260 11/48 Steiger zed- 129.9

TOBIAS E. LEOW, Primary Examiner. 

1. THE PROCESS FOR PREPARING ZINC 4-T-BUTYLTHIOPHENOXIDE READILY FILTERABLE IN AQUEOUS SOLUTION, WHICH COMPRISES MIXING IN AQUEOUS SOLUTION WITH VIGOROUS AGITATION A WATER-SOLUBLE SALT OF 4-T-BUTYLTHIOPHENOL AND A WATERSOLUBLE ZINC SALT, WHILE MAINTAINING A TEMPERATURE ABOVE 80*C. AND A MAXIMUM SOLIDS CONTENT IN THE RESULTING MIXTURE BETWEEN 25 AND 40 PERCENT, TO EFFECT A METHATHETIC INTERCHANGE BETWEEN TO TWO WATER-SOLUBLE SALTS WHEREBY ZINE 4-T-BUTYLTHIOPHENOXIDE IS FORMED AS A READILY FILTERABLE WATER-INSOLUBLE SALT, AND RECOVERING SAID ZINC SALT. 